Various high temperature materials have been developed for use in gas turbine engines. Cobalt-base and nickel-base superalloys have found wide use in the manufacture of gas turbine engine components such as nozzles, combustors, and turbine vanes and blades. Other materials, including niobium-based alloys, have been considered for the high temperature regions of gas turbine engines, such as the exhaust section. For example, on the basis of promising acceptable levels of fracture toughness and creep resistance, silicide-based composites toughened with a niobium-based metallic phase (e.g., NbTiHfCrAISi solid solution) have been investigated for applications where blade surface temperatures may exceed 1200 C. However, niobium and its alloys generally do not exhibit a sufficient level of oxidation resistance and creep performance at elevated temperatures. For this reason, niobium-containing materials intended for high temperature applications have typically required an oxidation-resistant coating, particularly if operating temperatures will exceed about 800 C. Commercially-available fusion coatings based on, in weight percent, Si-20Fe-20Cr have been proven effective in improving the oxidation resistance of niobium-base alloys. However, the fusion (reaction bonding) process must be conducted at about 1400 C., which can be detrimental to the alloy. In addition to the above, the Si-20Fe-20Cr alloy has not proven to be suitable as an oxidation-resistant coating for niobium-containing silicide-based composites.
It would be desirable if a silicide-based composite, and particularly one toughened with a niobium-based metallic phase, were available that exhibited improved oxidation resistance at temperatures of at least 1200 C., to enable such a material to be used in the hot section (turbine and exhaust) of a gas turbine engine without an oxidation-resistant coating. It would be further desirable if the niobium-based metallic phase were balanced with the intermetallic phases to provide a balance of high temperature strength and low temperature toughness.